Different oil recovery techniques have been developed to extract hydrocarbon fuels from subterranean geological formations. Most conventional oil recovery techniques can be classified into three categories, which include the primary technique, the secondary technique and the tertiary, or enhanced oil recovery (EOR) technique. The primary technique, which uses natural reservoir pressure or gravity to drive oil into the well bore, results in a recovery rate of about 10 percent for the original oil in place (OOIP). Secondary technique, which injects water or gas in the reservoir to displace oil and drive it into the well bore, results in about 20 to 40 percent recovery rate for the OOIP. Tertiary technique, or EOR technique, uses several different approaches to achieve higher recovery rate of about 30 to 60 percent, and may be characterized into three sub-categories that include thermal recovery, gas injection, and chemical injection.
The thermal recovery EOR technique involves the introduction of heat, such as the injection of steam, to heat the crude oil, thus lowering the viscosity of the crude oil, and facilitating the flow of crude oil through, e.g., pores and cracks in the rock formations for increased production. The gas injection EOR technique uses gases, such as natural gas, nitrogen, or carbon dioxide (CO2) to increase the pressure and decrease the viscosity of hydrocarbon fuels for improve oil flow. The chemical injection EOR technique injects chemicals into the reservoir to lower the surface tension that often prevents oil droplets from moving through a reservoir, which may increase, e.g., the effectiveness of waterflooding. Each of these conventional techniques has been hampered by its relatively high cost and, in some cases, by the unpredictability of its effectiveness.
Hydraulic fracturing, or fracking, is a relatively new recovery technique which induces fractures in the rock formations by injecting high-pressure fracking fluid (primarily water, containing sand or other proppants suspended with the aid of thickening agents) into a wellbore. Fractures, or cracks, in the deep-rock formations formed by fracking allow natural gas and petroleum to flow more freely. The early fracking recovery rate for gas was in the 2 to 5 percent range and improved to a current recovery rate of about 20 percent. The limited numbers available to date for oil well fracking indicate approximately a 5 to 6 percent recovery rate of oil.
There is a need for system and methods that can be used to supplement or replace existing oil recovery techniques that have improved recovery rates, and are environmentally friendly.